1. Field of the Invention
This invention relates to a system for producing a foamed article, in particular to a system for producing a foamed article having a great number of very small cells from thermoplastic synthetic resin having nucleated cells, and a molten resin preparing apparatus and a molding apparatus for use in such foamed article production system.
2. Description of the Related Art
There has been known a system for producing a foamed article by molding a gas-dissolving-resin in a molten state as a material into a mold to produce a variety of molded articles, as disclosed in, e.g., Japanese Patent No. 2625576 (corresponding to U.S. Pat. No. 5,158,986). In the system, carbon dioxide is introduced in a molten thermoplastic synthetic resin to cause the carbon dioxide into a supercritical state under conditions greater than critical temperature and pressure to prepare a material for a foamed article, namely gas-dissolving-resin, and the thus prepared material is supplied to a mold to produce a molded article.
Since the above system does not use a blowing agent (chemical substance) which resultantly forms cells in a molded article, the diameter of cell in a resultant molded article is extremely small in the range from 0.1 to 10 xcexcm. The diameter of cells in a foamed article produced from the above-mentioned material is as small as {fraction (1/10)} to {fraction (1/100)} compared to that of a foamed article produced from material having blowing agent. The thus produced foamed article is light in weight without impaired physical properties of synthetic resin.
The aforementioned system adopts a so-called injection molding technique in which a material for a foamed article is injected by an injecting apparatus into a mold space of a mold which is a jointed member of an upper die and a lower die. The mold space of a certain capacity is defined by the upper die and the lower die.
In the above system employing the injection molding technique, when material having nucleated cells (hereinafter, referred to as xe2x80x9ccell nucleatorsxe2x80x9d) is supplied into the mold space of the mold, a phase separation of carbon dioxide making cell nucleators occurs owing to a lower pressure in the mold space of the mold. Such cell nucleators grow into microcells as time lapses. Since the cell diameter are in an inversely proportional with the pressure lowering rate, it is required to regulate the pressure lowering rate in the mold to secure cells of extremely small diameter. In view of this, the conventional system is provided with a pressure regulator for giving a counter-pressure to the mold space to regulate the pressure lowering rate in the mold.
The pressure regulator comprises a gas cylinder containing carbon dioxide therein, a gas supply pipe connected to the gas cylinder and the mold space of the mold, and an openable/closable valve provided at the gas supply pipe. The pressure regulator regulates the pressure in the mold space of the mold to properly set a pressure lowering rate in the mold by controllably opening the valve.
Providing the pressure regulator in the aforementioned manner makes it difficult to manipulate the valve in an attempt to set the pressure lowering rate properly, thereby obstructing production of molded articles having uniform quality, also raising the production cost.
It is an object of the present invention to provide a system for producing a foamed article which is free from the problems residing in the prior art.
According to an aspect of the invention, a preparing apparatus prepares a molten gas-dissolving-resin having a great number of cell nucleators by diffusing a gas in a synthetic resin in a molten state under conditions of a predetermined temperature and a predetermined pressure. A molding apparatus foams and molds the gas-dissolving-resin supplied from the preparing apparatus into a foamed article having a great number of cells, the molding apparatus including at least two mold members which define a mold space and are movable relative to each other.
These and other objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed description and accompanying drawing.